[gcc r16-924] For datarefs with big gap, split them into different groups.

[hongtao Liu]

https://gcc.gnu.org/g:1bc5b47f5b06dc4e8d2e7b622a7100b40b8e6b27

commit r16-924-g1bc5b47f5b06dc4e8d2e7b622a7100b40b8e6b27
Author: liuhongt <hongtao.liu@intel.com>
Date:   Tue Mar 11 18:40:07 2025 -0700

    For datarefs with big gap, split them into different groups.
    
    The patch tries to solve miss vectorization for below case.
    
    void
    foo (int* a, int* restrict b)
    {
        b[0] = a[0] * a[64];
        b[1] = a[65] * a[1];
        b[2] = a[2] * a[66];
        b[3] = a[67] * a[3];
        b[4] = a[68] * a[4];
        b[5] = a[69] * a[5];
        b[6] = a[6] * a[70];
        b[7] = a[7] * a[71];
    }
    
    In vect_analyze_data_ref_accesses, a[0], a[1], .. a[7], a[64], ...,
    a[71] are in same group with size of 71. It caused vectorization
    unprofitable.
    
    gcc/ChangeLog:
    
            PR tree-optimization/119181
            * tree-vect-data-refs.cc (vect_analyze_data_ref_accesses):
            Split datarefs when there's a gap bigger than
            MAX_BITSIZE_MODE_ANY_MODE.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.dg/vect/bb-slp-pr119181.c: New test.

Diff:
---
 gcc/testsuite/gcc.dg/vect/bb-slp-pr119181.c | 15 +++++++++++++++
 gcc/tree-vect-data-refs.cc                  |  7 +++++++
 2 files changed, 22 insertions(+)

diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-pr119181.c b/gcc/testsuite/gcc.dg/vect/bb-slp-pr119181.c
new file mode 100644
index 000000000000..b0d3e5a3cb8b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/bb-slp-pr119181.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+void
+foo (int* a, int* restrict b)
+{
+    b[0] = a[0] * a[64];
+    b[1] = a[65] * a[1];
+    b[2] = a[2] * a[66];
+    b[3] = a[67] * a[3];
+    b[4] = a[68] * a[4];
+    b[5] = a[69] * a[5];
+    b[6] = a[6] * a[70];
+    b[7] = a[7] * a[71];
+}
+
+/* { dg-final { scan-tree-dump-times "optimized: basic block" 1 "slp2" { target vect_int_mult } } } */
diff --git a/gcc/tree-vect-data-refs.cc b/gcc/tree-vect-data-refs.cc
index 9fd1ef296506..f2deb751ed92 100644
--- a/gcc/tree-vect-data-refs.cc
+++ b/gcc/tree-vect-data-refs.cc
@@ -3682,6 +3682,13 @@ vect_analyze_data_ref_accesses (vec_info *vinfo,
 		      != type_size_a))
 		break;
 
+	      /* For datarefs with big gap, it's better to split them into different
+		 groups.
+		 .i.e a[0], a[1], a[2], .. a[7], a[100], a[101],..., a[107]  */
+	      if ((unsigned HOST_WIDE_INT)(init_b - init_prev) * tree_to_uhwi (szb)
+		  > MAX_BITSIZE_MODE_ANY_MODE / BITS_PER_UNIT)
+		break;
+
 	      /* If the step (if not zero or non-constant) is smaller than the
 		 difference between data-refs' inits this splits groups into
 		 suitable sizes.  */